The topic of this report is the identification and approximation of crosstrack structures present in sidescan sonar images obtained during sea trial MINEX-87. Three methods were developed to approximate this structure: piecewise polynomial approximation, Langrangian interpolation, and polynomial fitting by least square error. In each method, one variable parameter was permitted to account for changes in water column depth. The best method, which was based on the assumption that crosstrack structure is directly proportional to water column depth, proved to be the least square polynomial approximation. In this case, an average of traces, whose water column had been removed by an appropriate change of variables, was found. The polynomial fitted to this average adjusted its shape according to changes in water column depth. The success of this approximation was then measured by its ability to eliminate crosstrack structure when removed from traces in an image.